[Pw_forum] Functionals, pseudopotentials, etc. for H2O ice

[Nicola Marzari]

> 
> in the end, you are probably best off starting with some
> simple benchmark calculations to see how well the available
> choices (pseudopotentials, functionals, parameters) fit your 
> requirements and how much performance you are willing to sacrifice 
> for how much additional accuracy.



Thanks Axel for all the comments.

Steve - the H and O PBE RRKJ3 pseudopotentials from the pwscf
distribution are as accurate as they come. DFT using local/semi-local
GGAs is only partially satisfactory in the description of
water or ice; even more than exchange-correlatione effects,
though,  zero-point motion can be very important, and sometimes
proton tunnelling.

As Axel mentioned, there is a wide body of literature on
water and ice - you could check the papers by the Parrinello
group on both systems, and *especially* two recent (2004) JCPs
of Galli and coworkers. If you'd like to compare some of your
own results, we have a recent JCP (Sit and Marzari 2005) with
Espresso (pwscf and cp) calculations, using the above-mentioned
pseudopotentials.

Best,

			nicola

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